Field of the invention
This invention relates to a magnetic recording/reproducing apparatus using magnetic tapes or magnetic discs for data back-up applications.
b) Background Art
Magnetic recording/reproducing apparatuses capable of recording data that do not contain clock pulses on a recording medium such as a magnetic tape or a magnetic disc, checking the recorded data and retrieving selected data are already known. FIG. 6 shows the reproduction circuit of such an apparatus.
In a magnetic recording/reproducing apparatus of this type, data that d(i not contain clock pulses can be recorded on a recording medium by a magnetic head and any of the data stored in the medium can be reproduced by the head 1. The electric signals for the data reproduced by the magnetic head 1 then go through an amplifier and a reproduction circuit 2 having a filter and are converted into corresponding read data pulses by a read data generating circuit 3. A variable frequency oscillator 4 produces read data and window data out of the read data pulses received from the read data generating circuit 3. Formatter 5 is constituted by a host system comprising a computer and discriminates the positions of the read data by using the window data from the variable frequency oscillator 4 and determines if the data are normal.
Where a RAW (read after write) system is involved, after the magnetic medium is moved a given distance on the magnetic head to record data, the medium is moved back and caused to pass by the magnetic head for a second time to reproduce and check the recorded data. If an error is found, the above process of data recording and reproduction is repeated to eliminate the error.
Where a RWW (read while write) system is used, on the other hand, the magnetic medium is moved a given distance either on a magnetic head having two channels or on two magnetic heads so that the data recorded by one of the channels or the heads are reproduced immediately after the recording by the other channel or head for error checking. If any error is detected, the above process of data recording and reproduction is repeated to eliminate the error.
The follow-up characteristics of the variable frequency oscillator 4 and therefore the relationship between the level of external disturbances applied to the read data pulses from the read data generation circuit 3 and the gain of the circuit will be typically such as shown in FIG. 7. In the frequency range where external disturbances are high, the circuit remarkably loses its follow-up capability.
Any of the data stored in the magnetic medium of the above apparatus can be reproduced by the magnetic head 1 and the signals for the reproduced data are then transmitted by way of the reproduction circuit 2 to the read data generation circuit 3, where they are converted into corresponding read data pulses. The variable frequency oscillator 4 produces read data and window data out of the read data pulses from the read data generation circuit 3 and the formatter 5 discriminates the positions of the read data by using the window data from the variable frequency oscillator 4. The follow-up characteristics of the variable frequency oscillator 4 for data reproduction are invariable and are identical with those for data recording.
Japanese Patent Publication Sho 64-17263 discloses a magnetic recording/reproducing apparatus comprising a variable frequency oscillator having two different sets, of follow-up characteristics that allow the operation of error detection to be conducted only in a frequency range where errors are liable to occur during data reproduction. The purpose of this operation is to detect a deteriorated portion of a disk so that that portion may be avoided during recording. During normal read and write operations, however, the filtering quality of the variable frequency oscillator is not changed.
With a magnetic recording/reproducing apparatus as described above with respect to FIG. 6, however, if the formatter 5 determines that the recorded data do not contain any error even if an ISV (instantaneous speed variance) is detected near the upper limit of the follow-up frequency range of the variable frequency oscillator 4 during data recording, it can later reverse its judgment and determine that the data contain an error because the variable frequency oscillator 4 cannot follow-up the ISV when the data are reproduced sometime later. The drawback may be remedied by broadening the width of the follow-up frequency range of the variable frequency oscillator 4 but such a broadened follow-up range is inevitably accompanied by the problem of deterioration of recorded data over a wide frequency range that results in incompatible magnetic media and the loss of feasibility.
The follow-up characteristics of the variable frequency oscillator 4 can vary from supplier to supplier and also from apparatus to apparatus to adversely affect the compatibility of magnetic media, entailing frequent occurrences of errors of the type described above.
It is therefore a primary object of the present invention to provide a magnetic recording/reproducing apparatus which is free from the above problems and can significantly reduce the frequency of occurrence of errors due to ISVs during data reproduction so that the compatibility of magnetic media and the quality of recorded data can be remarkably improved.